The invention relates to an air conditioning system for motor vehicles. In particular, the invention relates to an air conditioning system for motor vehicles, which are driven by an internal-combustion engine equipped with an overrun fuel cut-off, and having a compressor driven by the internal-combustion engine for setting a defined desired evaporator temperature, along with a control or automatic control influencing the operation of the air conditioning system as a function of the operating condition of the internal-combustion engine.
Such an air conditioning system is known from German Patent document DE 199 14 443 A1. Here, as a function of the operating condition of the internal-combustion engine, the air conditioning system is controlled differently such that the compressor drive is switched on in the coasting operation of the internal-combustion engine and is switched off in other operating conditions, for example, while accelerating. As a result, on the one hand, the energy expenditures for the air conditioning system and thereby also the fuel consumption of the motor vehicle are reduced considerably and, on the other hand, the power of the internal-combustion engine is to largely be available for achieving the highest possible driving performance of the vehicle. Such an air conditioning system has the disadvantage that, in the compressor operation, control can take place precisely only to a predefined desired evaporator temperature, as a rule 1.6° C. When the compressor is switched off, the temperature will rise.
It is an object of the invention to provide an improved air conditioning system which permits a further reduction of fuel consumption and has a more positive influence on the driving dynamics of the vehicle.
According to the invention, this object is achieved by an air conditioning system for motor vehicles, which are driven by an internal-combustion engine equipped with an overrun fuel cut-off, and having a compressor driven by the internal-combustion engine for setting a defined desired evaporator temperature, along with a control or automatic control influencing the operation of the air conditioning system as a function of the operating condition of the internal-combustion engine. The compressor is an externally automatically controlled compressor with an adjustable swash plate for the variable adjusting of the evaporator temperature. The control or automatic control is operatively configured such that, in a coasting operation of the internal-combustion engine, the swash plate is adjusted such that the evaporator temperature is lowered below the defined desired evaporator temperature. Advantageous further developments are described herein.
An air conditioning system with an externally controlled compressor is an air conditioning system in which the evaporator temperature can be variably adjusted from the outside by adjusting the swash plate. By controlling the swash plate between a minimal and maximal inclination angle, it becomes possible to raise or lower the evaporator temperature to an arbitrary temperature level. When the inclination angle of the swash plate is enlarged, the suction pressure of the taken-in refrigerant is lowered and, as a result, the evaporator temperature is reduced. Correspondingly, when the inclination angle of the swash plate is reduced, the suction pressure and, connected therewith, the evaporator temperature, are raised again. The larger the inclination angle of the swash plate, or the wider the swash plate is open, the more refrigerant flows into the compressor, and the cooler the evaporator. In contrast to internally controlled compressors, the evaporator may not only be controlled to a defined evaporator temperature—the desired evaporator temperature—but also to an arbitrary evaporator temperature.
The air conditioning system according to the invention has the advantage that, in the coasting operation, in which the internal-combustion engine consumes no fuel, as a result of an enlargement of the inclination angle of the swash plate, the suction pressure is lowered and the evaporator temperature is therefore also lowered below the desired evaporator temperature down to the use of the anti-icing for the duration of the coasting operation without fuel consumption. Thus, additional coldness can be stored in the evaporator, which may later be released again. Simultaneously, as a result of the enlargement of the inclination angle of the wash plate, the engine braking effect is additionally increased.
For lowering the evaporator temperature, the swash plate is advantageously adjusted such that a maximal swash plate angle occurs. As a result, a maximal lowering of the evaporator temperature becomes possible without additional fuel consumption. The engine braking effect is also maximal. The maximal swash plate angle may differ as a function of the vehicle speed and/or other operating parameters.
Advantageously, the control of the air conditioning system may be further developed such that, after the coasting operation of the internal-combustion engine, the swash plate is adjusted at least for a certain time such that the evaporator temperature, which had been lowered below the desired evaporator temperature, rises again. As a rule, the coasting operation is followed by an acceleration operation. It may also be a constant operation. As a result of such a control, all power or a large portion of the power of the internal-combustion engine is available for the drive, for example, during the acceleration phase, which, in turn, has a positive effect on the driving dynamics of the vehicle. The raising of the evaporator temperature takes place while taking into account measured values which permit a comfortable evaporator temperature rise. The measured values are, for example, the outside temperature and/or the adjusted fan stage. The time window, in which such a control is carried out, should in each case be selected such that, after the termination of this control, the evaporator temperature will not be greater than the desired evaporator temperature. If necessary, fluctuations of the evaporator temperature are compensated by the heat exchanger temperature and/or the temperature mixing flap.
For raising the evaporator temperature, the swash plate is advantageously minimally opened for a defined first time interval, whereby the entire power of the internal-combustion engine is available for the drive during this first time interval. This first time interval is to be selected such that, also in the case of a subsequent minimal opening of the swash plate, the evaporator temperature does not exceed the desired evaporator temperature. Advantageously, the end of the first time interval is defined as a function of the actually determined evaporator temperature and/or the gradient of the evaporator temperature and/or the defined desired evaporator temperature. The greater the gradient of the evaporator temperature, the earlier the position of the swash plate has to be changed from the minimal opening before the desired evaporator temperature is reached. For reaching the evaporator temperature, after the defined first time interval, the swash plate is then advantageously adjusted such that the defined desired evaporator temperature occurs again.
Advantageously, the evaporator, whose desired evaporator temperature is set, is a coldness-storing evaporator, whereby the efficiency or the effect of the air conditioning system according to the invention can be increased. As an alternative thereto, the extra refrigerating capacity may be stored in a separate coldness-storing medium or in an external coldness storage device.
In the following, the invention will be explained in detail by way of a drawing.